2016 Volume 18 Issue 3+4 Pages 101-107
The prefrontal cortex, which is critical for temporal organization of the cognitive processes, is among the last cortical regions to reach full functional maturity. Prefrontal functions therefore show an unusually long period of vulnerability in which neurons and glia are easily affected by internal and external insults. Furthermore, early frontal lesions can result in deficits that are not immediately apparent, but predispose to later developmental problems such as learning disabilities, attention deficit/hyperactivity disorder, and even problems with moral judgment.
To fully appreciate the implications of developmental problems in children with frontal lobe damage, hypothesis-driven studies are needed to explore functions such as working memory or executive function during childhood, instead of sole reliance on traditional intelligence tests. Two functionally and neurally distinct cognitive selection mechanisms involve the prefrontal lobes:those based on internal representations （context dependent）;and those involving exploratory processing of novel situations （context independent）. We used a cognitive bias task representing contextual reasoning to correlate lateralization with age in the frontal lobes. Young children showed context-independent responses representing right frontal lobe function, while adolescents and adults showed context-dependent responses implicating left frontal lobe function. The locus of frontal cortical control in right-handed male subjects thus shifts from right to left as cognitive contextual reasoning develops.
In daily life, we repeat decision-making from several choices consciously or unconsciously. To make decisions and perform under uncertain circumstances, deliberation about possible future consequences using probabilistic estimations of both reward and risk is required. Recently, Damasio ［Behav Brain Res, 41, 81-94, 1990］ proposed the somatic marker hypothesis （SMH） as an explanation of the processes of human decision-making. In normal controls, sympathetic skin response （SSR） always appeared 1.5～2 s after the presentation of aversive/immoral visual stimuli. However, SSR did not appear in a patient with disconnection between the orbitofrontal lobe and amygdala. Failure of a contribution of the frontal-emotional circuits to decision-making could explain patient behavior （i.e., conduction disorder）. This finding seems to be in agreement with SMH.
Our studies suggest that frontal lobe functions develop gradually, with spurts between 5 and 10 years of age, reaching completion by post-adolescence. Frontal lobe function thus shows increased vulnerability and plasticity in the second decade of life.
